The son of billionaire mining magnate Gina Rinehart has lashed out at cabinet minister Barnaby Joyce’s “dangerous” intervention in the court battle over a $5 billion trust.

[cryout-pullquote align=”center” textalign=”center” width=”33%”]”This character sits three chairs down from the Prime Minister. To have someone so easily manipulated, or alternatively so naive, is dangerous in such a position”[/cryout-pullquote]

John Hancock, the estranged son of Australia’s richest person, on Thursday won an epic legal battle over control of the family trust, with his sister and ally Bianca Rinehart appointed trustee.

The judgment cited two letters sent by Mr Joyce and the now retired Liberal MP Alby Schultz to Mrs Rinehart’s other daughter, Hope Welker.

Mr Hancock said on Friday that Mr Joyce had questions to answer and raised doubt over whether he was should continue serving as a minister.

“Is this the type of person who should be sitting in federal cabinet?” Mr Hancock told Fairfax Media.

John Hancock. Photo: Bohdan Warchomij

Mr Hancock said that, by using his government email address to send an email urging Mrs Welker to drop the court action, Mr Joyce had involved the Abbott government in the dispute.

“This character sits three chairs down from the Prime Minister. To have someone so easily manipulated, or alternatively so naive, is dangerous in such a position,” he said.

“By doing so, he endorsed the conduct of Gina Rinehart and involved the Australian government.”

Mr Joyce was the Coalition’s regional development, local government and water spokesman when he emailed Mrs Welker on September 11, 2011.

The email noted he has “never met you” but stressed “Australia needs strong families and Hope we need, really need, yours to be strong”.

“Your family are good people, if they were not I would not care as much about you and your mum,” the email continued.

“You are a family Australia needs. All good families have their problems but before it gets really out of hand, I would try to get it back in house and out of public view.”

The note was sent from Mr Joyce’s parliamentary email address. He now serves as Agriculture Minister.

Mr Joyce and Mrs Rinehart have a long-standing friendship. The businesswoman was present for Mr Joyce’s maiden speech in the House of Representatives after the 2013 election and she flew him as a guest to a lavish wedding ceremony in India in 2011.

Of the email, Mr Hancock told Fairfax Media: “That pressure from his government email to someone he never met, on a subject he knew nothing about, apart from what had been fed to him, is extraordinary and means either he was manipulated to take such action, or he naively thrust himself in matters beyond his comprehension. Either way, [it is] a very dangerous example of his character for all Australians, given he is three seats down from the PM.

“The question then is, what other actions has this puppy dog made either due to outside manipulation or gross naivety?”

Mr Joyce and Mr Schultz have been approached for comment.

Mrs Rinehart’s Hancock Coal donated $22,000 to the Liberal Party and $5000 to the ALP in 2011/12.

In 2012/13, Hancock Coal gave $55,000 to Labor and $45,000 to the Nationals. Hancock Prospecting gave $55,000 to the Nationals and $8250 to Queensland’s LNP.

An executive at Hancock Prospecting has previously said the donations had nothing to do with Mrs Rinehart directly.